1. Field of the Invention
Generally, the present disclosure relates to the field of integrated circuits, and, in particular, to integrated circuits including resistors.
2. Description of the Related Art
Integrated circuits typically include a large number of circuit elements, which form an electric circuit. In addition to active devices such as, for example, field effect transistors and/or bipolar transistors, integrated circuits may include passive devices such as capacitors, inductivities and/or resistors.
Types of resistors that may be provided in integrated circuits include resistors that are formed from a layer of material that is deposited on a surface of a substrate, for example, on a surface of a region of the substrate wherein an electrically insulating material is provided. The region of the substrate including the electrically insulating material may include, for example, a trench isolation structure including, for example, silicon dioxide that is provided in a trench formed in a semiconductor wafer or die.
For reducing the number of material layers that must be deposited and/or patterned in the formation of an integrated circuit, it has been proposed to use material layers that are deposited over a semiconductor structure for forming gate electrodes of field effect transistors also for forming resistors. Conventionally, gate electrodes of field effect transistors have been formed of polysilicon. A polysilicon layer deposited on a substrate may be used for forming resistors over portions of a substrate, for example, over trench isolation structures provided adjacent active regions of field effect transistors. Over the active regions of the field effect transistors, gate electrodes may be formed from the polysilicon layer.
A resistance of a resistor formed from a polysilicon layer may depend on a sheet resistance of the polysilicon layer. The sheet resistance of the polysilicon layer may be controlled by doping the polysilicon layer, which may, for example, be performed by implanting ions of a dopant such as, for example, boron into the polysilicon layer.
For improving the performance of integrated circuits, it has been proposed to employ high-k metal gate (HKMG) technology for the formation of field effect transistors in integrated circuits. According to the high-k metal gate technology, silicon dioxide, which has been conventionally employed as a gate insulating material in field effect transistors, is replaced by a high-k material having a greater dielectric constant than silicon dioxide, for example, hafnium dioxide or hafnium silicon oxynitride. Using a gate insulation layer including a high-k material may help to increase the gate capacitance while, at the same time, avoiding leakage currents through the gate insulation layer.
Above the gate insulation layer including a high-k material, a gate electrode is provided. The gate electrode may include a first material layer and a second material layer. The first material layer is provided closer to the gate insulation layer than the second material layer, and may include a metal and/or a metal compound. The second material layer may include polysilicon. Providing the first layer including a metal and/or a metal compound between the high-k material of the gate insulation layer and the polysilicon of the second material layer may help to provide a work function of the gate electrode that is suitable for a field effect transistor including a gate insulation layer including a high-k material.
However, using first and second material layers that are provided for forming gate electrodes of field effect transistors in integrated circuits wherein the high-k metal gate technology is employed also for the formation of resistors may have issues associated therewith, as will be explained in the following.
For forming a resistor, contact structures may be provided at a surface of the second material layer including polysilicon that is opposite to an interface between the second material layer and the first material layer. The metal and/or metal compound of the first material layer may reduce the sheet resistance of the resistor, and may limit the highest obtainable sheet resistance value, even if the polysilicon layer is only weakly doped or substantially undoped, since there may be a path for an electric current between the contact structures through the first material layer.
It has been proposed to address the above-mentioned issue by removing portions of the first material layer in areas wherein resistors are to be formed before the deposition of the second material layer. However, this may increase the cost of the manufacturing process, increase the number of photolithography processes and, accordingly, the number of photolithography masks required, and may reduce the yield of the manufacturing process.
The present disclosure provides devices and methods wherein the above-mentioned issues may be avoided or at least reduced.